Yuquan Iron Pagoda, one of the Key National Cultural Relic Protection Units, is seriously corroded. Exploring the corrosion mechanism of its surface and the corrosion evolution process could provide technical support for subsequent conservation and restoration of the iron pagoda. By analyzing the surface atmospheric corrosion of modern cast iron within 1 300 days and that of the iron pagoda after 963 years, a structure of the corrosion layers of the cast iron within 1 300 days of atmospheric corrosion and that of the iron pagoda after 963 years were explored. Additionally, a corrosion model of Yuquan Iron Pagoda suitable for the cast iron with a long period (963 years) was deduced according to the abovementioned structures. The morphology, composition, corrosion layer structure of the surface corrosion products of the cast iron and iron pagoda samples were analyzed by means of the weight measurement and digital photography, SEM, XRD and laser Raman spectrometry. Moreover, the corrosion resistances of the samples were tested by electrochemical impedance spectrometry. The results show that the corrosion weight loss and corrosion time accorded with power exponential function. The corrosion products of cast iron and iron pagoda were composed of Fe₃O₄, γ-FeO(OH), α-FeO(OH), α-Fe₂O₃, and the early corrosion was mainly distributed in thin water film. Besides, the later corrosion product layers were distributed in several layers. The α/γ value of measurable rust layer protection and the corrosion resistance of the corrosion layers were gradually increased. The decreases of the contents of γ-FeO(OH) and Fe₃O₄ and the increase of the content of α-FeO(OH) were the main reasons for the structural transformation of cast iron and iron pagoda corrosion layers.